Bastille Day was last week and in tardy celebration the Loeb has set off a forty-four year old Romains candle, which not surprisingly fizzled. Dr. Knock, by French playwright Jules Romains, has reached the compulsory retirement age.

The play concerns a doctor who has just bought a small and unpromising country practice. First day on the job, he begins to implement his own theory of medicine. Healthy people are sick people who don't know it. One patient after another marches into his office, and with about as much trouble as it takes to persuade an arsonist to set a fire, Dr. Knock convinces each one that he is a near-invalid. Within weeks, the doctor has half the town in bed and a fortune in fees.

This comedy is regarded as a minor classic in France. On the theory that misery loves company, it is easy to see how French audiences might take the play to their hearts, not to mention their livers. A nation of hypochrondiacs might well find it plausible and even grimly amusing to watch Dr. Knock make the well ill. But Boston's large English-speaking sector will no doubt find it a silly bore.

Jules Romains' play is as tightly constructed as a Chinese puzzle, and just as wooden. He has even turned the sure-fire stage trick of Before and After into a dull science. We see a fresh-air mountain town transformed into a germ-crazy health spa. We watch a number of perfectly sound people subject themselves to two minutes of Dr.Knock's patter and turn into stretcher cases. But the one gimmick is pursued with such lethal, plodding logic that it nearly kills the play.

And with the same diligence, M. Romains makes every character comic, with nary a serious foil--which is something like painting a picture without an inch of void.

The cast, finding itself with shallow, mechanical parts, has retaliated by only going through the motions. Even Laurence Senelick's lines, which he lets go with a luscoius roll, somehow land with a clunk. Bea Paipert makes a very funny cow of an old lady, Kathryn Walker gives a droll, nasal performance of a declining aristocrat, and Tom Jones is perfect as a timid schoolteacher. But Director George Hamlin's overall pace is funeral, and most of the performances lack snap. The audience, however, seemed to enjoy the same mechanical trick of "getting sick" five or six times in a row.

The production is chiefly of interest to students of scenic design. John Braden's lush imagination has ushered forth a superb French rococco doctor's office and an oversize roadster, whose potboiling sound effects drown out many of the lines in the first act. Of course, Mr. Braden is often putting on a show of his own, but in the desolate land of witless farce, the set designer is king.